1. Field of the Invention
The present invention relates generally to a dual mode mobile phone, and in particular, to a circuit for maximizing a power rate of an RF (Radio Frequency) power amplifier.
2. Description of the Related Art
In a mobile phone, an RF power amplifier consumes much more power than other elements. Therefore, the RF power amplifier chiefly causes a reduction in battery run-time and it generates heat.
In addition, in dual mode phones, when the mobile phone switches its operation mode from an analog communication mode to a digital communication mode, the RF power amplifier is required to have high linearity.
The increase in linearity of the RF power amplifier causes a decrease in power rate, thereby causing a reduced battery run-time problem and a heat generation problem in the mobile phone.
In general, a dual mode mobile phone supporting both a CDMA (Code Division Multiple Access) mode (or a digital communication mode) and an AMPS (Advanced Mobile Phone Service) mode (or an analog communication mode) shares one RF power amplifier for the two modes. That is, an RF power amplifier for the CDMA mode is also used in the AMPS mode, to cut down the cost and the size of the mobile phone. However, when used in the AMPS mode, the RF power amplifier for the CDMA mode has a lower power rate, as compared with the RF power amplifier for the AMPS mode. Actually, the RF power amplifier for the CDMA mode has a power rate of about 30%, while the RF power amplifier for the AMPS mode has a power rate of over 50%. However, when used in the AMPS mode, the RF power amplifier for the CDMA mode has a power rate of 35-40% at most. This great reduction in efficiency of the RF power amplifier during AMPS mode is required in the prior art if reduction on cost and size is desired.
In addition, RF power amplifiers are classified according to the modulation mode. An RF power amplifier with a Model No. RI23124, though it is an RF power amplifier for the CDMA mode, can also be used in the AMPS mode. This RF power amplifier has an output power of 4 dBm to 30 dBm in the AMPS mode, whereas it has an output power of −50 dBm to 30 dBm in the CDMA mode. Further, the RF power amplifier discontinuously operates at full, ½, ¼ or ⅛ rate, according to the traffic conditions. Therefore, when operating in the AMPS mode, this RF power amplifier generates a great deal of heat and, thereby consumes a great deal of power.
However, the RF power amplifier does not require a high level of linearity when operating in the AMPS mode, as compared with the case when operating in the CDMA mode. Therefore, when it is possible to increase the power rate to some extent it is preferable to share the RF power amplifier between the AMPS and CDMA operating modes.